Now, your turn. Chances are you too have driven while drowsy. Sleep researchers at the Liberty Mutual Research Institute in Hopkinton, Mass., estimate that every day 250,000 Americans drive while sleep-deprived.

According to National Highway Traffic Safety Administration figures, more than 6,000 people are killed every year in vehicle accidents blamed on an exhausted driver behind the wheel. That's second only to drunk-driving fatal accidents and ahead of those attributed to driver distraction, which includes texting.

For someone operating a motor vehicle, sleep deprivation can be as dangerous as driving intoxicated.

Just one sleepless night or chronic sleep deprivation causes all kinds of problems, and not just while driving. A lack of adequate sleep affects a person's judgment, memory and emotional mood.

A recent study reported in the Journal of the American Medical Association put the annual dollar figure for workplace accidents associated with sleep deprivation at $31 billion.

If you go onto YouTube you will find plenty of videos of workers snoozing on the job. They're usually played for laughs -- like the video of a New York City subway worker sound asleep while the people videotaping cackle hysterically. But being exhausted at work or while driving a car is no joke.

"Sleep is such a powerful drive," said Dr. Meir Kryger of the Yale Sleep Medicine Clinic in New Haven, Conn. "If you need it, the brain will say 'Sleep' and that can be an incredibly dangerous situation."

Experts say most people need seven to eight hours of sleep a night. If you're one of them and you aren't getting it, you could fall asleep at work -- maybe not that big of a deal if you have a desk job (aside from embarrassment if your colleagues catch you at it), but if you're operating heavy machinery or driving a 2,000-pound car at 60 miles an hour, you've got a problem.

In addition to the prospect of falling asleep, there's another, insidious phenomenon called micro-sleep that can happen when you're very tired.

Micro-sleep occurs when you nod off for a second or a few seconds, often without even being aware of it. In some instances, your eyes may even be open and you can perform a task as if on a kind of auto-pilot, but you're asleep.

"Micro-sleep is a brief transition from wakefulness to sleep and it can last up to maybe 20 or 30 seconds," said Dr. Charles Czeisler, chief of theDivision of Sleep Medicine at Brigham and Women's Hospital. "You're awake and then suddenly you're asleep."

I wanted to learn more about the effects of sleep deprivation on driving and to experience for myself. So, an ABC News crew and I traveled to the institute's offices outside of Boston. Before we arrived, I stayed awake for 32 consecutive hours to mimic the effect of a sleepless night or chronic sleep deprivation.

At the lab, I was hooked up to a brain wave monitor and a device that tracks eye movement.

Then, I got behind the wheel of the researchers' minivan.

My assignment: to try to drive on their closed track for two hours while members of the research team rode inside the vehicle with me and studied my reactions.

As tired as I was, I still thought I would be OK. After all, I'd pulled many an all-nighter in college and many more in my years as a reporter.

But I hadn't driven 10 minutes before I felt myself fading.

The boredom of being on a closed track -- about 1/8 of a mile in length with two loops at each end -- exacerbated my fatigue. I could feel my eyelids drooping. My head started to slump. Soon, I found that I had been driving for brief stretches without any memory of it. Still, I pressed on.

About 20 minutes in, I suddenly awoke to find that I was off the track and driving on the grass next to it.

Shocked, I yanked the steering wheel and brought the vehicle back onto the road. I was scared and adrenaline was now pumping through me, bringing me to full wakefulness. It would not last long.

Soon, I was again feeling groggy and had increasing difficulty keeping the minivan in the middle of the paved road.

I was now going down a steep path toward unconsciousness but I struggled to continue. I was making the mistake many drivers make, convincing themselves they can go just a little further to their destination.

"We often delude ourselves into thinking that we decide whether or not we're going to go to sleep," Czeisler said. "'I'm just going to go another 10 miles. It's only half an hour to my house.' When you build up enough sleep pressure, you automatically make that transition to go to sleep. It can happen in the blink of an eye."

I drove an hour and then I just could not go on.

"In the words of [boxing great] Robert Duran, 'No mas,'" I said, pulling off the road and putting the transmission into park. "I'm done."

Back in the lab, Czeisler showed me just what had been going on in my brain while I'd been driving.

Pointing at the jagged lines on a chart propped on an easel, he said: "This is evidence that you're falling asleep."

He showed how my brain waves revealed the onset of sleep again and again. Then he ran a finger along the lines corresponding to my eyes blinking more and more slowly -- another tell-tale sign of the fatigue that had been washing over me.

I asked about the episode when I had run off the road.

"Yes," he said. "We could see it coming in your brain wave recoding."

He said I was asleep five or six seconds. But what truly shocked me was when he told me that I'd micro-slept a total of 22 times. I had only remembered dosing off twice.

I was lucky. I had been in a highly-controlled situation with safety precautions while driving just 15 to 30 miles an hour.

Every day, thousands of sleep-deprived Americans go whizzing along at speeds of up to 70 miles an hour. Many of them are aware they're exhausted but they are convinced -- as I was -- that they can outrace their own fatique.

Too often, it's a race they lose.

Yes, coffee and other forms of caffeine can stave off sleep, but only for a while. The only real solution: Pull over where it is safe and take a nap.